Nigerian Emeka Obi and Italian Gianluca Di Nardo were found guilty of international corruption and each given four-year jail sentences, three sources with knowledge of the ruling said.

Lawyers for Obi and Di Nardo declined to comment.

The long-running case revolves around the 2011 purchase by Italian oil company Eni and Anglo-Dutch peer Royal Dutch Shell of Nigeria’s OPL 245 offshore oilfield for about $1.3 billion.

Milan prosecutors allege bribes totaling around $1.1 billion were paid to win the license to explore the field which, because of disputes, has never entered into production.

The main trial - which besides Eni and Shell also involves Eni CEO Claudio Descalzi and four ex-Shell managers including former Shell Foundation Chairman Malcolm Brinded - is expected to drag on for months.

But Obi and Di Nardo, accused of being middlemen and taking illegal kickbacks, had asked for a separate fast-track trial which, under Italian law, allows sentences to be cut by a third.

Thursday’s ruling will not tie the court’s hand in the main trial.

But Barnaby Pace, anti-corruption campaigner at Global Witness, said: “This judgment will send shivers down the corporate spines of the oil industry.”

In an emailed statement, a spokeswoman for Shell said neither Obi nor Di Nardo worked on behalf of the company, adding it was waiting to see the fast-track judge’s written decision.

“Based on our review of the Prosecutor of Milan’s file and all of the information and facts available to us, we do not believe that there is a basis to convict Shell or any of its former employees of alleged offences,” it said.

Also in emailed comments, Eni reiterated it had acted correctly in the purchase of OPL 245, saying it had worked directly with the Nigerian government.

Nigeria’s OPL 245 is one of the biggest sources of untapped oil reserves on the African continent with reserves estimated at 9 billion barrels.

Eni, the biggest foreign oil producer in Africa, has been doing business in Nigeria since 1962 and last year produced 109,000 barrels of oil equivalent per day.

Shell is the biggest foreign investor in the country, producing 266,000 barrels of oil equivalent per day in 2017.

The sources said the Milan judge had ordered the seizure of $98.4 million from Obi and more than 21 million Swiss francs ($21.9 million) from Di Nardo.

Prosecutors had alleged Obi received a mandate from former Nigerian oil minister Dan Etete to find a buyer for OPL 245, collecting $114 million. Di Nardo, they said, took $24 million of that amount for putting Obi in touch with Eni.

The next hearing of the main trial involving Eni, Shell and 13 people is set for Sept. 26.

($1 = 0.9611 Swiss francs)